LED

lead

n.2

c.1300, "action of leading," from lead (v.1). Meaning "the front or leading place" is from 1560s. Johnson stigmatized it as "a low, despicable word." Sense in card-playing is from 1742; in theater, from 1831; in journalism, from 1912; in jazz bands, from 1934.

lead

v.2

early 15c., "to make of lead," from lead (n.1). Meaning "to cover with lead" is from mid-15c. Related: Leaded (early 13c.); leading.

Meaning "to be in first place" is from late 14c. Sense in card playing is from 1670s. Related: Led; leading. Lead-off "commencement, beginning" attested from 1879; lead-in "introduction, opening" is from 1928.

lead

n.1

heavy metal, Old English lead, from West Germanic *loudhom (cf. Old Frisian lad, Middle Dutch loot, Dutch lood "lead," German Lot "weight, plummet"). The name and the skill in using the metal seem to have been borrowed from the Celts (cf. Old Irish luaide), probably from PIE root *plou(d)- "to flow."

Figurative of heaviness since at least early 14c. Black lead was an old name for "graphite," hence lead pencil (1680s) and the colloquial figurative phrase to have lead in one's pencil "be possessed of (especially male sexual) vigor," attested by 1902. Lead balloon "a failure," American English slang, attested by 1957 (as a type of something heavy that can be kept up only with effort, from 1904). Lead-footed "slow" is from 1896; opposite sense of "fast" emerged 1940s in trucker's jargon, from notion of a foot heavy on the gas pedal.

LED

[ĕl′ē-dē′, lĕd]

Short for light-emitting diode. An electronic semiconductor device that emits light when an electric current passes through it. They are considerably more efficient than incandescent bulbs, and rarely burn out. LEDs are used in many applications such as flat-screen video displays, and increasingly as general sources of light. See also semiconductor laser.

lead

[lĕd]

Pb

A soft, ductile, heavy, bluish-gray metallic element that is extracted chiefly from galena. It is very durable and resistant to corrosion and is a poor conductor of electricity. Lead is used to make radiation shielding and containers for corrosive substances. It was once commonly used in pipes, solder, roofing, paint, and antiknock compounds in gasoline, but its use in these products has been curtailed because of its toxicity. Atomic number 82; atomic weight 207.2; melting point 327.5°C; boiling point 1,744°C; specific gravity 11.35; valence 2, 4. See Periodic Table. See Note at element.